N-(acyl)- $$\textit{N}^\prime $$ N ′ -(ferrocenylidene)hydrazines and their nickel(II) complexes: Syntheses, structures and physical properties

Abstract

The Schiff bases N-(acyl)- $$N^{\prime }$$ -(ferrocenylidene)hydrazines (HFcah (1) and HFcbh (2), where acyl = acetyl in 1 and benzoyl in 2 and H represents the dissociable amide proton) were synthesized in high yields (74 and 81%) by condensation reactions of equimolar amounts of ferrocene-carboxaldehyde and the corresponding acylhydrazines in presence of acetic acid in refluxing methanol. Reactions of $$\text {Ni(OAc)}_{2} \cdot \hbox {4H}_{2}\hbox {O}$$ , the Schiff bases (1 and 2) and $$\hbox {NaOAc}\cdot \hbox {3H}_{2}\hbox {O}$$ in 1:2:4 mole ratio in refluxing methanol afforded the diamagnetic iron(II)-nickel(II)-iron(II) species [ $$\text {Ni(Fcah)}_{2}$$ ] (3) and [ $$\text {Ni(Fcbh)}_{2}$$ ] (4) in 60 and 68% yields, respectively. Both Schiff bases and the two trinuclear complexes were characterized by elemental (CHN) analysis, mass spectrometric, various spectroscopic (IR, UV-Vis and $$^{1}\hbox {H}$$ NMR) and cyclic voltammetric measurements. Molecular structures of 2, 3 and 4 were determined by single crystal X-ray diffraction studies. The cyclopentadienide rings in the ferrocene moieties are essentially in eclipsed conformation in all three structures. Deprotonated Schiff base ligands in each complex ( $$\hbox {Fcah}^{-}$$ in 3 and $$\hbox {Fcbh}^{-}$$ in 4) act as five-membered chelate ring forming azomethine-N and amidate-O donors and assemble a square-planar $${ trans}\hbox {-N}_{2}\hbox {O}_{2}$$ coordination environment around the nickel centre. The redox active 1–4 exhibit an iron centred redox couple in the potential range 0.23–0.50 V (vs. Ag/AgCl). N-(acetyl/benzoyl)- $$N^{\prime }$$ -(ferrocenylidene)hydrazines (HFcah and HFcbh) and their diamagnetic nickel(II) complexes [ $$\hbox {Ni(Fcah)}_{2}$$ ] and [ $$\hbox {Ni(Fcbh)}_{2}$$ ], each containing a bent iron(II)-nickel(II)-iron(II) array, were synthesised and characterised by analytical, spectroscopic and electrochemical measurements. Molecular structures of HFcbh and the two trinuclear complexes have been confirmed by X-ray crystallography.